The present invention relates to a control device for a power steering apparatus, wherein light power steering can be performed irrespective of travel conditions.
A conventional power steering apparatus is controlled such that working oil is supplied from an oil pump to a power steering unit through a solenoid valve in accordance with a vehicle velocity as plotted in FIG. 1 so as to provide a constant steering force in a wide velocity range. When a vehicle travels along a highway, the steering wheel is held substantially straight, and steering angles are small. However, when the vehicle travels along a mountain road having many steep curves, the steering wheel is often turned, and steering angles are large. Thus, in FIG. 2, when a flow rate required for normal driving on an average city road is represented by a curve a, a flow rate required for driving on a highway where a low flow rate is required by a curve b, and a flow rate required for driving on a mountain road where a high flow rate is required by a curve c. Therefore, three characteristics are stored in a memory. A proper characteristic is read out from the memory so as to control power steering.
However, the steering force is also changed in accordance with a load. In order to keep the steering force constant if the load changes, there must be different characteristics for different loads. If heavy, intermediate and light loads are set, nine characteristics must be prepared and a large-capacity memory is necessary, resulting in increased cost.